Synthesis and characterization of biocompatible ZnFe₂O₄ nanoparticles for magnetic particle imaging (MPI)

Magnetic nanoparticles (MNPs) have significant interests in a wide range of medical applications, such as a tracer agent in magnetic particle imaging (MPI), contrast enhancement in magnetic resonance imaging (MRI), photothermal therapy treatment, and drug delivery systems. Zinc ferrites (ZnFe₂O₄) were synthesized by hydrothermal and co-precipitation methods. In this study, the effects of capping agents on the structural morphology, and magnetic behaviors of ZnFe₂O₄ nanoparticles were evaluated for MPI applications. The Fourier transform infrared spectroscopy ensured the presence of capping agents on the structures. The X-ray diffraction technique was used to characterize the structural properties of the synthesized samples. The crystallite size of single-phase cubic spinel zinc ferrite nanoparticles was maintained within 14–18 nm with the effect of capping agents. All synthesized ZnFe₂O₄ nanoparticles evaluated with the physical properties measurement method (PPMS) that showed superparamagnetic behavior. The capping agents polyacrylic acid, lauric acid, and malic acid played a significant role in the controllability of the nanoparticle size. A custom-designed magnetic particle relaxometer (MPR) at 9.9 kHz was used to evaluate the synthesized ZnFe₂O₄ for MPI applications. The MPR analysis of ZnFe₂O₄@PAA samples yielded the best results in terms of the shortest effective relaxation time (2.68 µs) and excellent spatial resolution (FWHM, 5.89 mT). The structural and magnetic characterizations of the zinc-based nanoparticles proved that they are suitable for MPI biomedical applications.